1. Field of the Invention
The present invention relates to a document copying machine which can consecutively feed copying paper from the stock section regardless of the movemental timing of the resist section.
2. Description of the Prior Art
In the case that copying is made with copying paper consecutively fed from the same stock section in the conventional document copying machine, it is so composed that a subsequent copying paper may begin being fed toward the resist roller from the stock section such as a paper feed cassette as soon as copying paper, which is located in the downstream of the transfer channel of the copying paper begins being fed toward the photosenstive drum by means of a resist roller (the secondary paper feeding roller) which constitutes the resist section.
In this case, in order to heighten the copying efficiency, the interval between a foregoing sheet of paper and a succeeding sheet of paper must be made shorter at the point where the sheets of paper pass through the transcribing portion. That is, it is necessary for the front end of succeeding sheet of paper to come up with the hind end of the foregoing sheet of paper, then the paper feeding speed of copying paper becomes comparatively high. For this reason, there remain such faults that the ratio of jam occurrence of copying paper is caused to become high in the transfer channel, and the ratio of failure occurrence to become high in the drive system.
On the other hand, another type of a document copying machine so composed that a still another resist section (the primary paper feeding roller) is provided at the upstream in the direction of transfer of copying paper and copying paper can be fed from the primary paper feeding roller to the secondary paper feeding roller when starting to feed the copying paper to the photosensitive drum from the secondary paper feeding roller has been developed. In this case, as it is possible for copying paper to be caused to wait for at the primary paper feeding roller, the transfer speed of copying paper in the transfer channel can be somewhat decreased.
Hereupon, in this case, as it is necessary that a primary paper feeding roller in addition to the secondary paper feeding roller and a clutch mechanism to turn on and off this primary paper feeding roller are newly provided, there is a still another fault that the cost of production is increased.
Therefore, recently, such a copying machine as copying paper is regularly fed from the stock section at a required interval of time in synchronization with the rotation speed of the photosensitive drum without waiting that copying paper passes through the secondary paper feeding roller on continuous copying has been developed, too.
In such a copying machine as shown in the above, as it is possible to feed copying paper at a speed in synchronization with the rotation speed of the photosensitive drum and with a fixed time interval, it is possible to carry out copying jobs quickly and with high efficiency at a comparatively slow speed of feeding the copying paper.
As the paper feeding speed can be made slow as shown in the above, the reliability of the copying machine can be enhanced and low-noise operation can be also accomplished. At the same time, a primary paper feeding roller and a clutch mechanism, which are necessary for securing a proper paper feeding timing in such conventional copying machines as shown in the above, can be curtailed, and a lowering of the cost of production can be accomplished, too. And in the case that the distance from the stock section to the resist section is very long, there may occur a case that the succeeding paper can not come up with the foregoing paper in the conventional copying machine having no primary paper feeding portion. Therefore, the copying number of paper per unit time may become uneven in the case of continuous feeding from one stock section and in the case of continuous feeding from the other stock section. However, as no influence may occur due to the distance of the paper feeding channel in such a method for continuously feeding copying paper from the stock section regardless of the operation timing of the resist section as shown in the above, the copying number of paper per unit time can be made uniform.
The limit of the copying number of paper in a copying machine is determined by the scanning capacity thereof, particularly the speed on which the optical system returns to the original position thereof after the scanning of a document is completed. The scanning capacity of the optical system is not uniform in every copying machine due to a drive motor itself of the optical system and fluctuation and/or imbalance of load on the drive motor and furthermore a lowering of the capacity by aging changes or temperature rise.
Therefore, when in such a copying machine shown in the above the scanning capacity of the optical system exceeds the transferability of the transfer mechanism of copying paper in the case of consecutive copying, the scanning for exposure must be waited for until the succeeding paper can be sent out from the resist section. So, the copying efficiency of the copying number of paper is decreased. On the other hand, when the scanning capacity of the optical system is lower than the transferability of copying paper as the paper feeding timing (timing on which paper is fed from the resist section) is determined by the scanning timing of the optical system, there may cause another problem that the copying number of paper which exceeds the fixed number of paper is fed in the transfer channel, and the succeeding paper is overlapped onto the copying paper which stops at the resist section.